1. Field of the Invention
The present invention relates to a method and a device that correctly detect a line-of-sight direction of a subject without contact.
2. Related Background Art
In order to correctly detect a line-of-sight direction of a subject without contact, information about coordinates of a pupil or an eyeball center in a three-dimensional space and an angle formed by a straight line connecting the coordinates thereof and a camera and a line-of-sight is required. Conventionally, a three-dimensional position of a pupil has been detected by the trigonometric method using two wide angle cameras (See, for example, Patent Document 1) or an eyeball center has been estimated by attaching at least three markers on a face (See, for example, Patent Document 2). However, aforementioned methods have problems such as needing at least two cameras, cumbersome camera calibration of stereo cameras.
An ultrasonic range finder is known as a method for finding a distance from a camera to a subject (See, for example, Patent Documents 3 and 4).
In this case, by mounting an ultrasonic transmitter close to a camera, emitting an ultrasonic wave, measuring a time required to return after reflecting on an eye, and multiplying the time by a velocity of the ultrasonic wave and dividing by 2, the distance from the camera to the eye can be determined. However, the distance to a pupil cannot be correctly measured by a TOF (Time of flight) method using such an ultrasonic wave, because the ultrasonic wave actually reflects in a wide range around an eye due to problems such as weak directivity of the ultrasonic wave.
[Patent Document 1] Japanese Patent No. 2739331
[Patent Document 2] Japanese Patent Application Laid-open No. Hei 10-066678
[Patent Document 3] Japanese Patent Application Laid-open No. 2003-186411
[Patent Document 4] Translated National Publication of Patent Application No. Hei 10-509933